Non-native teachers that teach English for example – or another language – have to maintain that tongue alive and fresh. How? By reading books or e-books in that language plus listening to a radio station on the Internet.
As well a learner of a second or foreign language can learn and acquire it by reading and studying grammar books and the linguistics of that tongue. I have a nice experience about that point. And it has helped me a lot.
Also the learner can play with the language, read in it, stop to think about it, more reading and studying, reading carefully, being curious about points about English – or another language, etc.
Yet in the classroom I advise you to teach with a communicative approach and methodology. English is learned and acquired by communicating in that language. I also have a nice experience about that point: my students can communicate in English because they have spoken a lot in it. / Photo from: YouTube